1. Simplified Surface Temperature Modelling
Jun Hao Koh, W. S. Koh
Abstract
Thermal load on buildings is the net accumulation of heat from the Sun, sky and surrounding surfaces in the built environment. In this study, a simplified 1D heat balance model was developed to provide an overview on the variation in surface temperature of conventional and high performance façade. This was done in conjunction with a simplified view factor and convective model. The model demonstrates good agreement with the overall trend of the measured surface temperatures throughout a day for two different industrial buildings. Virtual thermal performance evaluation of different façade materials is carried out to provide an insight on the effect of the potential retrofit of the existing building with high performance facade. An accurate prediction of the surface temperature will enable an accurate prediction of thermal comfort metric, such as mean radiant temperature, and expected impact of radiative thermal loading for different façade technologies in the tropical outdoor environment
Include Equation for convective term
Period of measurement (Transition monsoon season). Low convective resulting radiative component being the main contributor
Include only SF30% for Ayer Rajah
Have publication list in final report
Introduction
Results & Discussion
Heat Transfer in Urban System
Calibration of Model
Radiative Heat Transfer
Direct Solar Shortwave Radiation
Atmospheric Longwave Radiation
Longwave Radiation emitted from Urban surfaces
Convective Heat Transfer
Forced Convection (Wind from Environment)
Natural Convection (Temperature Difference)
Conductive Heat Transfer
Heat Conduction of thermal energy into building
H can be varied throughout the day to fit the modelled result with the measured data to compensate for the lack of information.
Water-proof concrete
SF-30% [4]
Mass density:
Conductivity:
Heat Capacity:
RMS error
1790Kg/m3
0.71 W/(m K)
880 J/(Kg K)
4.12
Different types of material can be used in the model to identify possible materials being used as the surface
1D Heat Balance Model
To determine surface temperature, a 1D Time-Dependent energy balance equation was used [1].
The Model was found to be able to capture the surface temperature trend of a horizontal surface with the measured irradiance data on that day.
Total radiation absorbed is contributed by Direct Solar, Diffused Sky, Atmospheric Longwave and radiation reflected and emitted by urban surfaces weighted by view factor.
Simplified Heat Convective model was used to describe natural convection occurring on the surface, where 𝐻 to be 5.6 as minimum value [2].
Surface temperature obtained from the model has shown to be in good agreement with the measured data (RMS < 2)
For South walls of Clean Tech One and Two, even though façade technology used are different, material of the façade used is key in surface temperature change throughout the day.
Objective
Site Implementation of Façade Technology
Calibration of model to experimented sites for both horizontal and vertical surfaces
Use of calibrated model to conduct a virtual site study on the thermal performance of different façade technology
Methodology
Experimented Site
View Factor Configuration
Simulated Surface temperature reach close to 60oC due to the highly conductive material of the façade.
Surface temperature reaches 2.5oC lower than the measured concrete surface. This could present possible reduction in urban heat island effect.
Simple Geometrical interface was used to describe the interface between the building and the surrounding (e.g. Tree Canopy and road)
Conclusion
Façade Technology
1D Time-Dependent Energy Balance model presents a fast method to predict surface temperature throughout a whole day with the irradiance as its primary data input.
The model is valid in condition where there is strong Solar irradiance and light wind.
Using the calibrated model, virtual surface temperature simulation can be carried out to evaluate the performance of various façade technology.
Aerial View of experimented sites. Solar radiation geometry between the sun and the sites were determined
Aluminum
Cross sectional view of the façade used by the buildings. Material of the façade was included in the implementation of the model
Acknowledgment
Model made use of the irradiance data collected at the rooftops used as inputs for the calculation of surface temperature.
View Factor was determined using numerical Monte Carlo Integration [3].
We would like to sincerely thank JTC and SMM Pte.Ltd. for making the site available for us to conduct the measurement.
References
[1] Çengel, Y. A. (2003). Heat transfer: A practical approach. Boston: McGraw-Hill.
[2] Qin, Y., & Hiller, J. E. (2013). Ways of formulating wind speed in heat convection significantly influencing pavement temperature prediction. Heat and Mass Transfer, 49(5), doi: /s
[3] Howell, J. R. (n.d.). A CATALOG OF RADIATION HEAT TRANSFER CONFIGURATION FACTORS. Retrieved from
[4] Asadi, I., Shafigh, P., Hassan, Z. F., & Mahyuddin, N. B. (2018). Thermal conductivity of concrete – A review. Journal of Building Engineering, 20, doi: /j.jobe